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Old 12-21-2017, 08:54 PM   #1
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Default Onan 2.8KV half Hz and Volts, shutdown after start released

Hi, My Onan 2.8KV series G ( in Roadtrek 210)
shuts down after start button released, runs otherwise with 1/2 voltage:

Checking voltage on VR connector, it runs at half volts and frequency:
Output on pins 2-3 : 60V ~25-30Hz
Pins 9-10, about 20V at the same 25-30Hz frequency
Resistance when disconnect from VR

resistance on 9-10 is 20 Omh ( disconnected)
Field Flash on Pin 7 is 12.2V

Not sure if this is faulty VR, slip rings , rotor or something else?
Obviously it shutdowns because of low voltage/Hz, but what is the cause of it.
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Old 12-21-2017, 08:57 PM   #2
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Does an error code pattern flash on the switch's LED?
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Old 12-21-2017, 09:00 PM   #3
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It does not have switch LED, other that on remote start. No codes there I could see.
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Old 12-22-2017, 03:31 AM   #4
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Quote:
Originally Posted by dessa View Post
It does not have switch LED, other that on remote start. No codes there I could see.
The codes do flash on the remote start switch. Watch it when it goes out. If your model does it, it will tell you exactly why it shuts off.
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Old 12-22-2017, 03:27 PM   #5
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If the frequency is running low the generator is running at reduced speed and you should check the governor linkage. See that it is moving freely when the engine is stopped. You could start on the local start switch at the generator and move the linkage manually to the approximate correct speed. If the power comes on at this point you have determined the problem.
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Old 12-22-2017, 05:50 PM   #6
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It it the same as opening throttle to to the max, right? Or does Onan 2.8KV governor works somehow else?

I believe when I've played with throttle, it sounded like RPMs went up, but frequency only when from 24 to just below 30... I will recheck again.

I also wonder if Magneto/ignition somehow could cause low RPM? If it is RPM but not some bad control board/VR.
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Old 12-22-2017, 11:38 PM   #7
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I had frequency problems once. It was caused by bumps on the slip rings and bouncing brushes leading to a melted brush holder. Just adding a datapoint. I have no idea what is causing your problems. I think the rotor has to be removed to check out the slip rings and brushes. Cummins Onan fixed it for me for $1600. Just thought I'd make your day!
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Old 12-23-2017, 12:29 AM   #8
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Before speculating too much, I think I would concentrate on the frequency being 1/2 of rated and not increasing.

Onan's set the frequency based on rpm, so you need to see what the rpm actually is. You can get relatively inexpensive inductive tachometers that run off the spark plug wire or an also inexpensive Harbor Freight or equivalent reflective tach. Normally, I would expect the engine to surge under load if the it is running short of fuel or spark, and it should speed up if you pull the throttle without load, although you need to make sure you are actually bypassing the governor and not just the balancing spring when you do it. if the engine is running at speed or close to it, you have basically put the issue on the generator or controlling circuit.

Others likely would know better than I do about how the windings are setup on the Onan, and if you lost a pole or set of poles, would you still get some frequency showing or not.

This is not the type of issue we usually here about with Onans, so not a lot of experience around, I think.
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Old 12-23-2017, 02:03 AM   #9
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Default low freq generator

The Onan is a 3600 RPM machine. That means it is a 2 pole machine making it unlikely that a pole winding has been lost. I feel that the most likely scenario is that it is running slow for some reason. To me this points to the governor or its attendant linkage, springs etc. It it is, indeed, running at half speed it is likely that the output voltage is low as well. The suggestion to find a tachometer is a good one because it would eliminate a speed problem. Are you certain of the meter that you are using to measure frequency?
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Old 12-23-2017, 02:04 AM   #10
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Definitely will try Tachometer! Great advise, thanks!
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